Much attention has recently been directed to the formation of fabric confinements requiring special characteristics. For example, the automobile industry has become increasingly concerned with safety of automobile occupants during a crash. It is known to construct a confinement, referred to as an "air bag" in an automobile which is inflated upon detection of a crash. Today, many automobile manufacturers have met consumer concern for safety through the inclusion of air bags in motor vehicles not only as optional equipment but also as standard equipment.
However, manufacturers have encountered difficulty and expense in the formation and production of air bags of specified shapes and dimensions.
A typical air restraint system presently utilized in passenger motor vehicles includes an inflatable confinement, or air bag, an impact detector and an inflating means. Upon detection of an impact greater in magnitude than a threshold impact, the impact detector provides a signal to the inflating means which causes the inflating means to inflate the confinement. The inflating means illustratively comprises pyrotechnic or gas producing means. Thus, the inflated confinement serves to protect the passenger and/or driver from what is often considered the most serious effect of an automobile collision: a secondary collision, i.e., the collision between an occupant and the interior of the motor vehicle.
Unfortunately, any such air restraint system is effective in preventing personal injury only to the extent that the occupant properly contacts the inflated bag. Thus, the dimensions and shape of an inflated air bag are critical and are often dictated by an exacting specification.
The specific shape and dimensions of any particular air bag are affected by the position in which it is placed in a motor vehicle. Consideration must be given to not only the position of the protected occupant(s) but also to the portion of the vehicle's interior in close proximity to the air bag and against which the air bag will be forced in a collision. Such design considerations, among others, have led to uniquely shaped air bags. For example, U.S. Pat. No. 4,262,931 to Strasser et al. discloses an air bag having a plurality of compartments for knee, torso and head restraint, some of which deploy towards one of the passenger seating positions and some of which expand laterally across the vehicle interior in front of the adjacent passenger position. This particular device also utilizes a pressure regulating valve flap between compartments. U.S. Pat. No. 3,937,488 to Wilson et al. depicts an elongated air bag of approximately rectangular cross-section and planar end sections. This particular device utilizes two different materials of different air permeability to form the air bag.
Some known devices have attempted to solve problems associated with providing air bags of precise shapes and dimensions through stitching together separate sheets of fabric so as to form a desired shape. Unfortunately, stitched seams in known air bags have encountered difficulty in maintaining the pressure within the bag during inflation. Air bags, in order to be effective, must inflate within a fraction of a second. Such a rapid rate of inflation and ultimate pressure leads to the exertion of a tremendous tensile load on the stitching. Such stitching decreases the overall strength of the fabric at the seam due to the perforations in the fabric inherent from the stitching process. Additionally, the strength of the stitching thread must be considered, as well as the additional cost of stitching.
Furthermore, stitching of separate sheets of fabric, whether they are identical or of different air permeability, increases the bulk of the air bag, as the seam will have a thickness which is at very least the sum of the thickness of both separate sheets of fabric. With the current practice of downsizing vehicles, any unnecessary bulk is most undesirable. Excess bulk leads to unwanted excess weight which is undesirable in efforts to reduce weight and which in turn makes rapid deployment more difficult. Stitching is also undesirable since it produces a protrusive stitched surface which may harm an occupant whom it contacts. Illustrative of air bags constructed from stitched together layers of fabrics is that disclosed in U.S. Pat. No. 3,892,425 to Sakairi et al.
For the sake of completeness, it has been recognized that air restraint bags which at least partially deflate soon after, or even during, inflation advantageously provide a means to counteract the dangerous effect known as rebound. Such controlled deflation permits the air bag to absorb more energy from the occupant.
Various methods have been proposed for the controlled deflation of air bags. Illustrative of such methods are those disclosed in U.S. Pat. Nos. 3,937,488 to Wilson (air bag constructed from at least two materials having different air permeability values) and U.S. Pat. No. 3,892,425 to Sakairi et al. (air bag constructed from coated material wherein expansion of the air bag stretches the stitches of the fabric, creating new openings through the coating in addition to microporous openings).
Additionally, the exacting specifications to which an air bag manufacturer must adhere to include requirements relating to shape, dimension, energy absorption, inflation and deflation time periods, toxicity, flammability, tensile and tear strength, flexibility from -30.degree. C. to 90.degree. C., temperature and accelerated aging resistance. Unfortunately, the use of fabrics can present difficulty in meeting such requirements.